1. Field of the Invention
This invention relates to a gauging system for measuring the level of a liquid in a tank using a capacitive probe.
2. Description of the Prior Art
Previously proposed capacitive gauging systems utilize a low impedance oscillator to drive a current through a capacitive probe, the magnitude of the current being proportional to the probe capacitance. This current is then amplified, converted to an A.C. voltage in a precision pre-amplifier, and then further converted in a precision A.C./D.C. converter into a D.C. voltage. Any required linearization is effected by extensive analog circuitry. A precision capacitor is used to nullify the capacitance of the probe corresponding to an empty liquid storage tank.
Such a gauging system using analog processing suffers from several disadvantages including the risk of large temperature-dependent errors in the analog circuitry and the generally high cost of precision analog components.
It is therefore an object of the invention to provide an improved liquid-level gauging system which requires fewer precision components and has a high degree of accuracy.